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Using APEX-1 and APEX-2 observations, we have detected and studied the rotational lines of the HC3N molecule (cyanoacetylene) in the powerful outflow/hot molecular core G331.512−0.103. We identified 31 rotational lines at J levels between 24 and 39; 17 of them in the ground vibrational state v  = 0 (9 lines corresponding to the main C isotopologue and 8 lines corresponding to the 13C isotopologues), and 14 in the lowest vibrationally excited state v 7 = 1. Using local thermodynamic equilibrium (LTE)-based population diagrams for the beam-diluted v  = 0 transitions, we determined T exc = 85 ± 4 K and N (HC3N) = (6.9 ± 0.8) × 1014 cm−2, while for the beam-diluted v 7 = 1 transitions we obtained T exc = 89 ± 10 K and N (HC3N) = (2 ± 1) × 1015 cm−2. Non-LTE calculations using H2 collision rates indicate that the HC3N emission is in good agreement with LTE-based results. From the non-LTE method, we estimated T kin ≃90 K, n (H2) ≃ 2 × 107 cm−3 for a central core of 6 arcsec in size. A vibrational temperature in the range from 130 to 145 K was also determined, values which are very likely lower limits. Our results suggest that rotational transitions are thermalized, while infrared radiative pumping processes are probably more efficient than collisions in exciting the molecule to the vibrationally excited state v 7 = 1. Abundance ratios derived under LTE conditions for the 13C isotopologues suggest that the main formation pathway of HC3N is C2H2 + CN → HC3N + H. [ABSTRACT FROM AUTHOR]

We report a centimetre-wave (cm-wave, 5–31 GHz) excess over free–free emission in planetary nebulae (PNe). Accurate 31- and 250-GHz measurements show that the 31-GHz flux densities in our sample are systematically higher than the level of optically thin free–free continuum extrapolated from 250-GHz. The 31-GHz excess is observed, within one standard deviation, in all 18 PNe with reliable 31- and 250-GHz data, and is significant in nine PNe. The only exception is the peculiar object M2-9, whose radio spectrum is that of an optically thick stellar wind. On average the fraction of non-free–free emission represents 51 per cent of the total flux density at 31 GHz, with a scatter of 11 per cent. The average 31–250 GHz spectral index of our sample is (in flux density, with a scatter of 0.14). The 31–250 GHz drop is reminiscent of the anomalous foreground observed in the diffuse interstellar medium (ISM) by cosmic microwave background (CMB) anisotropy experiments. The 5–31 GHz spectral indices are consistent with both flat spectra and spinning dust emissivities, given the 10 per cent calibration uncertainty of the comparison 5-GHz data. However, a detailed study of the objects with the largest cm-excess, including the low-frequency data available in the literature, shows that present spinning dust models alone cannot explain the cm-wave excess in PNe. Although we have no definitive interpretation of our data, the least implausible explanation involves a synchrotron component absorbed by a cold nebular screen. We give flux densities for 37 objects at 31 GHz, and for 26 objects at 250 GHz. [ABSTRACT FROM AUTHOR]